The mobile communication industry is facing an increasing demand for high data rate applications (e.g., video, multimedia, and so forth). To meet this demand, standards like High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) are being developed within the Universal Mobile Telecommunications System (UMTS) mobile phone standard. These higher data rates generally require better signal quality between a mobile device and a base station, where the mobile device may be a mobile phone and the base station may be a cellular tower.
The signal quality and range may be enhanced by increasing the number of base stations in order to reduce the maximum distance between a given base station and the mobile device. For example, in a cellular network system, increasing the number of cellular towers effectively decreases the distance between a given mobile device in the network and the nearest cellular tower. However, this solution would be cost prohibitive due in part to the high cost of installing and maintaining additional base stations.
The range of high data rate transfer within a communication system may also be increased using a primary antenna with a diversity antenna to create two receiver chains within the mobile device. According to a typical design, the primary antenna sends and receives signals, whereas the diversity antenna is dedicated to signal reception. The diversity antenna complements the primary antenna by preventing fading, where fading is defined by a reduction of signal quality and/or transmission rate.
The diversity antenna typically experiences an isolation effect with the primary antenna. The isolation effect may reduce the TX power of the signal that is received by the diversity antenna. A diversity antenna switch associated with the diversity antenna may be designed to take advantage of this isolation effect. For example, the so-called “front end” of the switch may be optimized by omitting typical primary filter components, such as the duplex filter and external low noise amplifier (LNA). Omitting these components results in cost and space savings, as well as other benefits.
Under normal operating conditions, the lack of the duplex filter and other front end components in the diversity receiver is acceptable due to the isolation that occurs between the primary antenna and the diversity antenna, which limits the signal power received by diversity antenna. However, under certain abnormal conditions, the isolation between the primary antenna and diversity antenna can be dramatically lowered. The abnormal conditions may be caused by placing the diversity antenna too close to, or on, a metal plate or by other abnormalities that the mobile device may experience. Under these and other abnormal conditions, relatively fragile and power sensitive components, such as a Surface Acoustic Wave (SAW) filter associated with the diversity antenna, may be exposed to power levels close to, or equal to, the fully transmitted signal power. The excessive signal power may damage or even destroy these components.